Manufacture of aliphatic anhydrides



June 27, 1933. H, DREYFUS ET AL 1,915,569

' AMANUFACTURE OF ALIPHATI ANHYDRIDES Filed June l5, 1928 /23 CONJGhSa/n E c Vesse/ Receiver- Attorneys Patented June 2?, 1933 ran HENRY DREYFUS, 0F LONDON, ENGLAND, AND CLFFORD VAN HANEY, OF DRMIVIOND- VILLE, QUEBEC, CANADA, ASSIGNOES T0 CELANESE CORPOB'ATQN 0F AMERICA,

A CORPORATON 0F DELAWARE MANUFACTURE or anim-tario aimYnnInns Application led .Tune 15, 1928, Serial No. 285,614, and in Great Britain July 15, 1927.

This invention relates to the manufacture of aliphatic anhydrides from aliphatic acids and especially to the manufacture of acetic anhydride from acetic acid.

lt `is known that aliphatic anhydrides can be produced by passing aliphatic acid vapour through tubes or other apparatus heated to high or relatively high temperatures. In such processes however, we have found that, especially after continued operation of the process at high temperatures, a certain amount of charring or decomposition to gasn eous products takes place.

)Ne have now found that this di'liiculty can be largely or entirely overcome if the aliphatic acid `vapour is subjected to pyrogenic reaction by mixing it with an inert gaseous medium heated to temperatures above those at which the aliphatic acid vapour is split to anhydride and water.

According to the invention therefore we produce aliphatic anhydrides (and especially acetic anhydride) by mixing aliphatic acid vapour (and especially acetic acid vapour) with an inert gaseous medium heated to temperatures above those at which the aliphatic acid is split to anhydride.

In performing the invention we may employ any inert gaseous medium, for instance, nitrogen, hydrogen, steam or superheated steam, the last mentioned being especially suitable. v

The splitting of the aliphatic acid vapour to anhydride by the process of the invention may be performed at any temperatures above the p oint of splitting of the aliphatic acid to anhydride, for instance at temperatures of from about 5000 to 12000 C. and preferably 5000 to 10000 C., and for this purpose the inert gaseous medium may, prior to admiX- ture with the aliphatic acid vapour, ,be heated to any temperature above the point of splitting of the aliphatic acid to anhydride, for instance to temperatures of from about 6000 to 1200" C. and preferably 8000 to 1200o C.

The aliphatic acid vapour may be mixed with the heated inert gaseous medium in any suitable manner; for instance, the aliphatic acid in liquid or vapour form,

and preferably in vapour form, may be injected into a stream of the heated inert gaseous medium, or for instance a stream of the acid vapour and a stream of the heated inert gaseous medium may each be passed into may with advantage be preheated to any temperature below that at which the splitting of the aliphatic acid vapour is to be performed. For instance, whenthe splitting of the aliphatic acid vapour is to be performed at temperatures over about 6000 C. the aliphatic acid vapour may with advantage be preheated to about 1500 to 3000 C.

The gases or vapours resulting from the admixture of the aliphatic acid vapour with the inert gaseous medium, and hereinafter referred to as the reaction vapours, may be treated in any suitable Way to recover the anhydride produced. In order to obtain the highest yield vof anhydride care should be taken to avoid condensation of the water vapour (present or produced by the reaction) with the anhydride, as if such condensation takes place the anhydride is to a greater or less extent hydrolyzed back to the acid with resulting diminution of yield of anhydride.

To avoid such condensation and to obtain the anhydride in as pure a form as possible the reaction gases or vapours may be subjected to fractional condensation, for instance by leading them upwards through one or more fractionating columns maintained at a temperature or temperatures intermediate between the boiling points (under the conditions of pressure obtaining) of water and of anhydride whereby the anhydride 'is condensed and the water passes on in vapour form. Or the reaction vapours may be passed through a solvent or mixture of solvents for the anhydride which have higher boiling points than water, and preferably of higher boiling points than the anhydride, and which are preferably insoluble in water, such solvents being employed at temperatures intermediate between the boiling points (under the conditions of pressure obtaining) of wa- CII --such bodies.

`tervapour by .the'vapouri'of oneor more en .training liquids.' '.Insuch form ofexecution.

Or the reaction vapoursmay for instance be subjected to condensation by the process described in our British Patent No. 303,772 and the corresponding U: S. application S. No.A

284,566 iiled June 11, 1928.v That is to say the anhydride may be condensedfromthere-V action vapours whilst carryingaway the wa- ""the reaction vapours are preferably mixed A-after leavingzthelhot reaction zone with the 'vapours of thezentraining liquid or, liquids' at a temperature-below the boiling point: (una derithe conditions 'ofzpressure' obtaining); of

f the anhydride. "Conveniently such mixingl may be' performed by introducing-.the reac- 4tion vapours (which should notbe allowed to coolbelowzthe -boiling'point of Water before fbecoming mixed with the vapoursv Vof. theen- Atraining liquid orliquids) into a vessel up` whichthe vapours of theentraining liquid orV anhydride; may :be 'substantially' condensed' vand the water 'vapour carried Iaway with the 'riva liquids'fare cause'dto4 rise; this means the oursfo'fzthe entraining liquid or'liquids, xam-ples of `entraining Iiqmdswhich 'we' may usefor such method of condensation are,

i as indicated in'ouri'said British Patent' No.

-`303',772'and theccorresponding U. S'.y appli! ;cati-o`i S.Y No284566-filedjune 11,1'1928, benzene, carbonI tetrachloride, petrol, mixi tures'oftwoor;more of such bdiesfor mix- 4 -'tures Aj'of' ether withr petroleum yether, it` will beA understood' however that any other liquids chemically-'inert to? vthe anhydride and hav? q iinga'high-entraining-capacityifor water may' beeniployed.""1The liquids should preferably Ahave a low entraining capacity for the ,an-L'Z ah'ydrfide. f

5'* Or there'action vapours -mayfo'r instance'I be' subjected' Ato condensation-bythe process described inJ our' British `Patent No.*298,667

aludcor-respending;` S.. application S-[Nog A285,613 lfiled Ju'ne'1 5,ff1928, that is to say they may be subjectedtofcondensation b'y-leading themu'nder the surface of anrextracting liquid-cooled down or otherwise kept at temperatures belowT (and preferably considerably 3 below) the boiling point vof water. As ex plained in our Asaid =British` Patent No.' 298,667

mean va' liquid on liquid mixture inv which the lanhydride issoluble' and lwhich i`s` chemically -inertto theoanhydrideiandinsoluble or sub tioned benzene, chloroform and mixtures of ethylether or chloroform with one or more hydrocarbons such as light paraiiins, gasoline, kerosene, benzol or it homologues. As stated inv our said British Patent. No;1298,667 and corresponding to Ui* S. application S. No. 285,613, We preferably use as extracting liquids, liquids of the. character referred to which are themselves hydrocarbons or'which contain nhydrocarbons, r`for example., benzene, or mixtures of'ethylether or chloroform with one ormorehydrocarbons such as paraiins (particularly the petroleum fraction of boiling point 40 to' YOOLCJ`- termed` petroleum ether) gasoline (boiling point to 90? (l), kerosene,benzol -or 'its-homologues. w`=r lhe following' p articular examples 'of extracting liquids have beenfoundto be very suitablez ether in admixtureO with'fpetroleum feather,

'chloroform -mixeds with petroleum ether and or gasoline ;v and mixtures lof* 4ether and petroleum 'fet-her contain-ing about l30 to 50% of-petroleum` ether are kespecially suitable.

1'" Or the reaction vapours may forinstance be'- treatedv by theprocess-described'intthe British PatentlNo=1289,972 `and the corresponding U. S. application Si No.A 242,9771of 27th December,f1927`, that isto saythey may maintained ata temperature or'temperatu-res below A (and f preferably .substantially below) f the temperature at whichfthe splittingo'f-the aliphatic acidva-pour isfperfornied'sv By such treatment the water vapour may'fbe-'substan ytially f absorbed `from l the reaction v vapours.

In such treatment the water binding substances are preferably maintained at temperiatures abovethe boiling pointinnder' the conditions of pressure obtaining) of-Water to avoid condensationfof 'water andthe' resulting risk of loss`of anhydride through'hy- `drolysis, and for the bestfunctiningof the treatment the vwater-l binding 'substances should be employed atftemperatures'above the boiling point of theanhydride in' which case the water can be substantiallylabs'orbed and the anhydride pass; on in vapourform. As explained in the said British" Patent "No. 289,972 and the corresponding U; S. applil cation SINO. 242,977 i of 27th December^1927 the `term f-water bindiiig"-substance means bisulphates,Vv pyrosulphate's' (especiallybisulphates and pyrosulphates ofthe alkali and earth alkali metals), vzinc= -hlor-ide,.- calciuni' chloride, orthopho'sphoric acid; A pyrophosphoric acid,l metaphosphoric acid Iand l-ike substances which havellaliinity 1 (a-'ndprefer `and-corresponding to U. S. application S. No." 1285,61?) bythe-term= 5extracting7 liquid we ably highafinity) for w-a-te'r but excluding substances `having a-de'leteriouseect on" ali# phatic acids or anhydrides, such as sul-phuric acid.

f The accompanying-drawing illustrates in diagrammatic fornrone form'ofexecution' of fthe invention, applied by wayfof'example to' 'l iit the manufacture of acetic anhydride from concentrated or glacial acetic acid, it being understood that they are given only by Way of illustration and are in no Way limitative.

Referring to the drawing the acetic acid is vaporized in the still 1 and the resulting vapours passed via the pipe 2 to the outer zone 3a of the heat exchanger 3, Where they are heated t a temperature of about 200-- 300 C., and pass thence via the pipe 4 into the reaction vessel 5 (of copper, earthen- Ware, vitreosil or other suitable material) in Which they are mixed with superheated steam 'supplied at a temperature of 800 to 1000 C.

by the pipe 6. The supply of the acetic acid vapour to the vessell 5 is controlled by the cock 7 to keep the temperature of the mixed vapours at 500 to 800 C. The vessel 5 is provided With bafiies 8 to ensure thorough mixing of the acid vapours With the superheated steam. The reaction vapours pass from the vessel 5 through the pipe 9 to the inner zone 3b of the heat exchanger 3 Where they are cooled to about 200 to 300O C. The reaction vapours pass from the inner zone 3?) of the heat exchanger 3 via the pipe 10 down below the surface of the extracting liquid (a mixture of ether and petroleum ether, for instance a mixture of equal volumes of ether and petroleum ether) 11 con- Y tained in a brine cooled or Water cooled vessel 12, the end of the pipe 10 carrying a rose or jet 13 to ensure that the reaction vapours are delivered into the extracting liquid in a state of fine division. The reaction vapours, before passing under the surface of the extracting liquid may if desired be mixed With the vapours of the ether/petroleum ether mixture; for instance, after leaving the inner zone 3b of the heat exchanger 3 they may pass to a vessel (not shown) interposed in the pipe 10 and to which the vapours of the ether/petroleum ether are supplied. The temperature of the reaction vapours, immediately prior to coming in contact With the extracting liquid is kept at a temperature above the boiling point of Water, for instance about 100-150 C. The extracting liquid is kept at a temperature of about 20 C. by circulation of cold Water or brine through the jacket 14, and gentle stirring is applied to the extracting liquid by means of the stirrer 15 to ensure uniformity of tempera.- ture in the liquid and to ensure that fresh extracting liquid is brought in contact with the incoming reaction vapours. The reaction vapours on issuing from the jet or rose 13 become condensed and the anhydride is separated from the Water to a very elicient extent, the anhydride (together With unconverted acetic acid) dissolving in the extracting liquid Whilst Water falls to the bottom of the vessel 12 and runs off through the pipe 16. The vessel 12 is provided With an outlet pipe 17 and a constant level run off 18 and by this means the extracting liquid containing the dissolved anhydride, is run 0E continuously via the pipe 17 and constant level 18 into the receiver 19.

The Water runs oliq from the vessel 12 70 through the pipe 16 and the pipe 20 to the run olf vessel 21, and in so doing is scrubbed by an ascending stream of extracting liquid fed by gravity from the tank 22 via the pipe 23 and the nozzle 24. The extracting liquid issues from the nozzle 24 in the form of a fine spray and passes up through the pipe 20 in the form of small drops and thence via the pipe 16 into the vessel 12; for convenience of observation the pipe 20 is made of glass. By means of this scrubbing very little anhydride or unconverted acid is carried avvav by the Wate;` and the Water can be run to Waste from the run off vessel 21.

instead of running the Water olf from the vessel 12 in the manner above described it may be run oif in any other desired manner. For instance it may be run ofi continuously from the bottom of the vessel 12 by means of a Florentine bottle as commonly employed in the essential oil industry and in the 1nanufacture of acetic anhydride.

The acetic anhydride may readily be recovered from the extracting liquid collected in the receiver 19, for instance the liquid so collected may be heated to distill oli' the extracting liquid.

It will be understood that the invention is not limited as to the strength of the a` i phatic acid employed. The process can be performed even With the vapours of Adilute acids; and besides affording a ready means for the manufacture of anhydride from` concentrated or highly concentrated acids, it affords valuable means for producing anhydrides from Waste or dilute acids, especially Waste or dilute acetic acids such as result from the acetylation of cellulose or other industrial acetylation processes.

TWhat We claim and desire to secure by Letters Patent is 1. Process for the manufacture of an aliphatic anhydride comprising subjecting an aliphatic acid vapor to pyrogenic decomposition by mixing it With an inert gaseous medium heated to a temperature above that at Which the aliphatic acid vapor is split to its anhydride and Water.

2. Process for the manufacture of acetic anhydride, comprising subjecting acetic acid vapor to pyrogenic decomposition, by mixing it With an inert lgaseous medium heated to a temperature above that at which acetic acid is split to its anhydride and Water.

3, Process for the manufacture of an aliphatic anhydride comprising subjecting the vapor of an aliphatic acid to pyrogenic decomposition by mixing it With supcrheated steam heated to a temperature above that at 100 which the aliphatic acid ivaporfis split to its anhydride and Water.

4. Process for the manufactureofacetic anhydride comprising snbjectingacetic acid Vapor to pyrogenic decomposition by mixing it with superheated steam heated to a temperature above that at which acetic acid is split to its anhydride and Water. n

5. Process for the manufacture of an aliphatic anhydride comprising subjecting the Vapor of an aliphatic acid to pyrogenic decomposition at a temperature bet-Ween 500o and 1000o C. by mixing it with an inert gaseous medium heated to a tempera-ture between 600 and 1200O C.

6. Process for the manufacture of acetic anhydride comprising subjecting acetic acid vapor to pyrogenicdecomposition at a temperature between 500D and 1000o C., by mixing it with an inert gaseous medium heated t0 a temperature between 600o and 1200 2 C.

7 Process for the manufacture of an aliphatic anhydride comprising subjecting the vapor of an aliphatic acid to pyrogenic decomposition ata temperaturefbetween 500 and 1000 C. by mixing it with superheated steamy heatedl to a temperature between 600 and 1200-o C.

anhydride comprising subjecting acetic acid vapor to pyrogenic decomposition at a ternperature betweeni500 and 1000" Cl'by mixing it with superheated steam heated to a temperature between 600Ov and 1200O C. t

9. In a process according to claiml, the step of heating the aliphatic acid-vapor toa temperature-below that at which the pyrogenie decomposition is to beperformedprior tormixing the aliphatic acid Vapor with the a 8l Process for theh manufacture of aceticl'm 

